Morphology of ultrathin Ag films grown on Mo(111)

Ultrathin films of Ag grown on Mo(111) and vicinal surfaces have been studi ed using temperature programmed Auger, LEED and thermal desorption spectros copy. We confirmed that Ag does not induce faceting of Mo(111) and growth o f Ag follows the Stranski-Krastanov mode as reported previously. In additio n, we found that (1) on top of the wetting layer; there is a two-dimensiona l (2-d) gas-like phase in coexistence with the Ag 3-d clusters. The density of this gas increases with temperature and can reach a very high value of about 0.8 monolayer at 900 K. (2) 2-d films deposited at 120 K show an anom alous coverage dependent stability against 3-d cluster formation. (3) If th e total coverage is not more than 0.3 monolayer above the wetting layer, th e film deposited at low temperature is unstable and 3-d clusters readily fo rm when annealed around 450 K. However, once annealed to 750 K, the 3-d clu sters fully re-spread and the 2-d film formed is trapped in a supersaturate d state, i.e. although its coverage is larger than the wetting layer, clust er formation no longer occurs whatever way we anneal it. Auger and LEED evi dences suggest that films annealed above 600 K undergo interface confined m ixing of Ag and Mo. (4) On the vicinal surface we studied, although nucleat ion of 3-d clusters can occur at a temperature 50 K lower than that on the singular surface, the density of the 2-d gas-like phase on the vicinal surf ace is basically the same as on the singular surface. (C) 2001 Elsevier Sci ence B.V. All rights reserved.